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| United States Patent |
5,268,398
|
|
Nakagawa
, et al.
|
December 7, 1993
|
Friction material and method of manufacturing such material
Abstract
A friction material is so manufactured that a hygienic environment can be
maintained while simultaneously reducing the brake noise without reducing
the friction coefficient of the brake pads made of the present material.
The friction material is granulated or agglomerated by a first binder
which binds one or more inorganic substances having a plane netlike
crystal structure into granules which are deformed so that the particles
have a flat particle orientation in the resulting granules. The flat
particle orientation is achieved by the application pressure and/or heat
during the formation. The granules are then embedded in a second binder
forming a fibrous matrix for forming the brake pad material. The inorganic
substance or substances forming the particles having the plane netlike
crystal structure, promote a microseparation in the friction surface in
response to the application of a brake force. The microseparation
effectively prevents brake noise.
| Inventors:
|
Nakagawa; Mitsuhiko (Itami, JP);
Yamashita; Yukinori (Itami, JP);
Ibuki; Masanori (Itami, JP);
Kishimoto; Hiroya (Itami, JP)
|
| Assignee:
|
Sumitomo Electric Industries, Ltd. (Osaka, JP)
|
| Appl. No.:
|
930500 |
| Filed:
|
August 17, 1992 |
Foreign Application Priority Data
| Sep 01, 1989[JP] | 1-228153 |
| Aug 29, 1990[JP] | 2-229091 |
| Current U.S. Class: |
523/158; 523/153; 523/155; 523/156; 523/157; 524/447; 524/449; 524/451; 524/495 |
| Intern'l Class: |
C08J 005/14; C08K 003/20; C08K 003/04 |
| Field of Search: |
524/447,449,451,495
523/153,155,156,157,158
|
References Cited
U.S. Patent Documents
| 4388423 | Jun., 1983 | Kaufman et al. | 523/153.
|
| 4403047 | Sep., 1983 | Albertson | 523/153.
|
| 4678818 | Jul., 1987 | Nakagawa et al. | 523/149.
|
| 4735975 | Apr., 1988 | Iwata et al. | 523/153.
|
| Foreign Patent Documents |
| 2142995 | Mar., 1973 | DE.
| |
| 54-34349 | Mar., 1979 | JP.
| |
| 57-37187 | Aug., 1982 | JP.
| |
| 59-4459 | Jan., 1984 | JP.
| |
| 64-4541 | Jan., 1989 | JP.
| |
| 2011448 | Jul., 1979 | GB.
| |
Primary Examiner: Michl; Paul R.
Assistant Examiner: Szekely; Peter
Attorney, Agent or Firm: Fasse; W. G.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation of application Ser. No. 07/696,623,
filed on May 7, 1991, now abandoned, which is a continuation-in-part of
copending application Ser. No. 07/575,671, filed in the U.S.A. on Aug. 31,
1990, now abandoned.
Claims
What we claim is:
1. A friction material having a friction surface, comprising a granular
component and a fibrous component, said granular component including
granules comprising a first binder and friction particles held together by
said first binder to form said granules of said granules component, said
friction particles having a plurality of layers formed as plane network
crystal structure layers interconnected along boundary surfaces in said
friction particles, said friction material further comprising a second
binder forming a matrix, said granular component and said fibrous
component being embedded in said matrix of said second binder, and wherein
said plane network crystal structure layers in said friction particles
have an orientation in said granules substantially in parallel to said
friction surface for reducing brake noise.
2. The friction material of claim 1, wherein said granules of said granular
component have a deformed oblong configuration so that said oblong
configuration granules also extend approximately in parallel to said
friction surface.
3. The friction material of claim 1, wherein said friction particles have
an oblong configuration.
4. The friction material of claim 1, wherein said friction particles held
together by said first binder in said granules include at least one member
selected from the group consisting of mica, talc, vermiculite, aluminum
hydroxide, magnesium hydroxide, agalmatolite, kaolin, chlorite, sericite,
iron hydroxide, montmorillonite and graphite.
5. A method for producing a friction material having a friction surface,
comprising the following steps:
(a) forming a granular material by mixing a first binder with friction
inorganic particles having a plurality of layers formed as plane network
crystal structure layers in said friction particles,
(b) mixing a second binder with said granular material and with a fibrous
material to embed said granular material and said fibrous material in said
second binder to form a deformable mixture,
(c) molding said deformable mixture into a shape desired for said friction
material, wherein granules of said granular material have an approximately
flat configuration, oriented parallel to said friction surface and
(d) grinding at least one surface of said shape to form said friction
surface.
6. The method of claim 5, wherein said molding step is performed with the
simultaneous application of heat and molding pressure to said deformable
mixture.
7. The method of claim 5, wherein said molding step is performed by the
application of heat to said deformable mixture.
8. The method of claim 5, wherein said molding step is performed by the
application of molding pressure to said deformable mixture.
9. The method of claim 5, further comprising curing of said desired shape
prior to said grinding.
10. The method of claim 5, wherein said granular material is formed by
agglomeration of said friction particles with the aid of said first
binder.
11. The method of claim 5, wherein said step of forming said granular
material comprises mixing said friction particles with said first binder
to form a mixture of crushable material, and crushing said crushable
material to form said granular material.
12. The method of claim 11, further comprising drying said mixture prior to
crushing.
13. The method of claim 5, wherein said grinding is performed so that said
approximately flat configuration of said granules extends substantially in
parallel to said friction surface in said friction material.
14. The method of claim 5, wherein said molding is performed so that said
plane network crystal structure layers of said inorganic particles extend
substantially in parallel to said friction surface.
Description
FIELD OF THE INVENTION
The present invention relates to friction materials and to a method of
manufacturing the friction material. Such friction materials are used in
disc brakes, drum brakes and the like of vehicles such as trucks and
automobiles.
BACKGROUND INFORMATION
Conventionally, a material which uses asbestos as a main friction material
is generally known for use in brakes for trucks, automobiles and the like.
However, there is a demand for friction materials not using asbestos from
the viewpoint of safety and hygiene Japanese Patent Laying-Open No.
54-34349, Japanese Patent Publication No. 64-4541, Japanese Patent
Publication No. 57-37187 and Japanese Patent Publication No. 59-4459
disclose conventionally and generally known friction materials not using
asbestos. Japanese Patent Laying-Open No. 54-34349, which corresponds to
U.S. Pat. Nos. 4,273,699 (Chester) and 4,310,452 (Chester) discloses a
friction material obtained by forming a mixture of phenol-formaldehyde
resin and fibers such as steel fibers or glass fibers and an inorganic
reinforcement material other than asbestos. Mica is listed as one of the
grain reinforcing materials.
Japanese Patent Publication No. 64-4541 discloses the use of mica as a
filler in a friction material using glass fibers and fused liquid
crystalline polyester as a matrix material of a polymer binder in order to
change the properties of the friction material and to reduce manufacturing
costs.
Japanese Patent Publication No. 57-37187 discloses a friction material
including a fibrous substance of 0-5 vol. %, scaly or layered mica of
20-60 vol. %, phenol resin of 5-30 vol. %, BaSO.sub.4 of 5-30 vol. %,
cashew dust of 5-15 vol. % and metal particles of 5-30 vol. %. It is
mentioned that mica can replace asbestos as a main friction material.
Japanese Patent Publication No. 59-4459 teaches mixing coke powder and
cashew dust as a friction material, whereby the coke powder becomes
enveloped with cashew dust or the coke powder is diffused in the cashew
dust.
The foregoing shows that a number of friction materials not using asbestos
have been conventionally proposed. However, no known material has been
developed that costs the same as an asbestos containing material and has
the characteristics of asbestos such as flexibility, strength, wearing
resistance and softness to provide a substitute for asbestos and
consequently a plurality of different fibers are used together to provide
a substitute for asbestos. However, most of the substitute fibers are
thick and stiff and have such characteristics that separation and
segregation between fibers and other powder material might occur dependent
on the treatment after mixing mica and other powder materials. Separation
and segregation prevent the formation of a homogeneous mixture.
In addition, since the powdery and scaly form of mica which can be used
effectively as a substitute for asbestos, can explode, it is very
difficult to form a homogeneous mixture. It is also difficult to mix mica
and the like with resin or the like used as a binder or matrix, whereby
the bonding between the mica and the binder may be insufficient, so that
the friction material has a lower strength or cracks may be caused by
expansions due to gas occurring during the formation and curing. Using an
increased amount of resin as the binder for avoiding these problems,
allows the heat resistance of the friction material to deteriorate,
thereby furthering the expansion due to gas formation. Hence, it is
difficult to manufacture a mica containing friction material of uniform
quality as an effective substitute for a friction material containing
asbestos.
Another conventional problem to be solved with respect to the
characteristics required of a friction material for brakes, is brake noise
occurring at the time of braking. It is difficult to effectively prevent
such brake noise. Generally, a friction material containing a large amount
of solid lubricant such as graphite is well-known as a friction material
which is unlikely to cause brake noise. However, if a large quantity of
graphite or the like is used, the friction coefficient .mu. is decreased
resulting in a lower braking force. Also effective for preventing brake
noise in braking, is a friction material containing a large quantity of
organic filling materials such as rubber and cashew dust, as is disclosed
in, for example, Japanese Patent Publication No. 59-4459 as mentioned
above. However, such friction material also has a decreased friction
coefficient .mu. when a brake is applied at a high speed. Such brake
materials also generate more than normal heat, thereby increasing wear and
tear.
U.S. Pat. No. 4,735,975 (Iwata et al.) discloses a brake pad material in
which the granular structure is rigid as will be described in more detail
below with reference to FIG. 12. Iwata et al. require this rigidness in
the granular structure to avoid deformation or disturbance of the granular
structure in the final thermal and pressure deformation applied for
forming the brake pad material. Such a rigid granular structure cannot
reduce brake noise because the particles within the granular structure are
not easily displaced relative to each other when a brake force is applied.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a friction material
which avoids using asbestos for environmental reasons and which solves the
brake noise problem by substantially reducing brake noise compared to
conventional brake material. The invention also wants to effectively
prevent a reduction of the braking force due to a decrease of the friction
coefficient. In other words, the invention aims at providing a brake
friction material that maintains its friction coefficient during operation
as a brake lining while still achieving a substantially reduced brake
noise.
Another object of the present invention is to provide a method of
manufacturing a friction material by which the environment is protected
and a friction material of uniform quality can be manufactured.
Briefly stated, according to the invention, the present friction material
includes friction particles, e.g., as granules that are approximately flat
for adjusting the friction coefficient, and the wear resistance.
Preferably, the friction particles which form the approximately flat
granules are inorganic substances including graphite formed as layers
having a plane network crystal structure for reducing brake noise. The
expression "friction particles" is used herein interchangeably with the
expression "inorganic substances including graphite. The inorganic
particles are so arranged that the separation between the crystal layers
of the inorganic particles occurs approximately in parallel to the
friction surface of the friction material. It has been found that this
effect substantially reduces the brake noise.
The friction material according to the invention comprises a granular
component and a fibrous component, said granular component including a
first binder and granules of inorganic particles held together by said
first binder to form said granules, said inorganic particles having a
plurality of layers formed as plane network crystal structure layers, and
a second binder forming a matrix, said granular component and said fibrous
component being embedded in said matrix of said second binder, and wherein
said plane network crystal structure layers in said inorganic particles
have an orientation in said granules substantially in parallel to said
friction surface for reducing brake noise.
The present friction material is produced as follows: forming a granular
material by mixing a first binder with inorganic particles having a
plurality of layers formed as plane network crystal structure layers in
said inorganic particles, by further mixing a second binder with said
granular material and with a fibrous material to embed said granular
material and said fibrous material in said second binder to form a
deformable mixture, by molding said deformable mixture into a shape
desired for said friction material, wherein said granules have an
approximately flat configuration; and by grinding at least one surface of
said shape to form said friction surface.
Forming the granular material for use in the friction material of the
present invention is preferably performed as follows. The inorganic
particles are mixed with a suitable first binder disclosed below. The
resulting agglomeration is crushed to form the required granules prior to
curing the agglomeration. It is important that the formed granules assume
an approximately flat oblong configuration.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be clearly understood, it will now be
described, by way of example, with reference to the accompanying drawings,
wherein:
FIG. 1 is a graph showing brake noise occurrence ratios of A-I brake pads
manufactured based on Table 2;
FIG. 2 is a graph showing, in addition to the brake noise occurrence ratio
of F-1 showing in FIG. 1, brake noise occurrence ratios of F-3, F-4, F-5,
F-6 and F-7 each singly equal in vol. % of mica and graphite measured
under the same condition of measurement as that of F-1 in FIG. 1;
FIG. 3 is a graph showing friction coefficient I in a test conducted by
using a dynamometer simulating a small sized car of 2000 cc in accordance
with an examination standard of JASO 6914;
FIG. 4 is a process diagram explaining a method of manufacturing disc brake
pads shown in Table 3;
FIG. 5 shows a plane crystal structure network of the inorganic substances
that are used in a friction material according to the invention;
FIG. 6 is a side view showing two layers each having a plane crystal
structure network of the inorganic substance of FIG. 5;
FIG. 7 is an enlarged view of a single friction particle formed of a number
of layers of an inorganic substance, whereby each of these layers has a
plane crystal structure network as shown in FIGS. 5 and 6;
FIG. 8 is an enlarged view of a friction granule formed of a plurality of
friction particles as shown in FIG. 7 embedded in a first binder material;
FIG. 9 is a mixture of friction granules as shown in FIG. 8 with a
reinforcing fibrous material in a second binder to form the friction
material of the invention;
FIG. 10 shows the friction material of FIG. 9 following a treatment causing
an orientation of the friction particles inside the friction granules
substantially in parallel to a surface that will become a friction surface
in the finished friction body of the invention;
FIG. 11 is a view similar to that of FIG. 10, but showing the plane
friction surface of a friction body according to the invention in which
the friction particles in the friction granules are oriented substantially
in parallel to said plane friction surface;
FIG. 12 is an enlarged sectional view of a conventional friction material
according to U.S. Pat. No. 4,735,975 (Iwata et al.) to be compared with
the present friction material as shown in FIG. 11; and
FIG. 13 is a block diagram illustrating the steps for making a friction
material body according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS AND OF THE BEST MODE OF THE
INVENTION
Table 1 shown in the following shows composition ratios of materials for
disc brake pads according to one embodiment of the present invention.
Table 2 shows 18 combinations (A, B, C1, C2, D1, D2, E, F1-7, G1, G2, H
and I) of a particle diameter of graphite, a particle diameter of mica, a
method of granulating graphite and mica, kinds and quantity of binder,
kinds of solvent and the like.
TABLE 1
______________________________________
Materials of Composition
Composition Ratios
______________________________________
kevlar (aramid pulp)
10 vol. %
copper powder 3 vol. %
glass fiber 10 vol. %
cashew dust 15 vol. %
molybdenum disulfide
2 vol. %
phenol resin 20 vol. %
graphite Y vol. %
mica X vol. %
calcium carbonate residual quantity
subtotal 100 vol. %
______________________________________
(Note)
In using the formed granulated substance of graphite and mica, the amount
of phenol resin equivalent to half the quantity of binder (vol) used in
the granulated substance is decreased. (Note) In using the formed
granulated substance of graphite and mica, the amount of phenol resin
equivalent to half the quantity of binder (vol) used in the granulated
substance is decreased.
The remaining half of the binder for granulation is not included in the
above described 100 vol. %.
TABLE 2
__________________________________________________________________________
A B C-1 C-2
D-1 D-2
E F-1
__________________________________________________________________________
mica 70.mu.
100.mu. 2.5 10 10 10 10 20 23
vol. % vol. %
500.mu.
graphite 270.mu.
100.mu. 4.5 5 5 7
vol. % vol. %
60.mu.
rotary pan
0 0 0 0 0
method of
extruding
granulation
roll
none 0 0 0
polyethylene
NBR NBR NBR
kind of binder phenol
polyethylene
glycol phenol phenol phenol
quantity of binder to
15 15 20 20 15
mica graphite vol. %
solvent trichloro- ethylene
H.sub.2 O H.sub.2 O
##STR1##
__________________________________________________________________________
F-7
F-3 F-4 F-5 G-1 G-2
H I
__________________________________________________________________________
mica 70.mu.
23
100.mu. 23 23 30 30 10 40
500.mu. 23
graphite 270.mu. 7
100.mu. 7 7 8
60.mu.
7
method of rotary pan 0 0 0 0
granulation
extruding
0
roll 0
none 0 0
kind of binder phenol
polyvinyl butyral
##STR2##
sodium alginate polyvinyl
alcohol NBR
vinyl acetate
quantity of binder to
15 12 12 15 40
mica graphite vol. %
vol. %
solvent
##STR3##
trichloro- ethylene
##STR4##
H.sub.2 O
H.sub.2 O
isopropyl
alcohol
__________________________________________________________________________
(Note)
Phenol is resol type water soluble resin and NBR is latex.
(Note)
F-6 is cured by heating for 5 Hr at a temperature of 200.degree. C. (F6
has the same composition as that of F3)
F-2 is the same as F1, and is a simple addition without granulation.
An example A for comparison does not contain any mica nor any graphite at
all and is not granulated. The conditions of formation of the disc brake
pad shown in Table 1 were as follows. The temperature at which
pressurization took place, was maintained at 160.degree. C. The
pressurization was applied for 10 minutes and the pressure was set so that
the completed pad may have a porosity of 10%. After this thermal formation
under pressure, the disc pad was heated in a furnace at 220.degree. C. for
10 hours to complete the curing and thereafter the pad was abraded to have
a prescribed thickness.
Referring to Table 2, the graphite used herein was natural graphite of
scaly-form made in Sri Lanka and mica was phlogopite produced in Canada,
both of which are suitable for the present purposes as substances having
plane crystal structure network as shown in FIGS. 5 and 6. Inorganic
substances having the plane crystal structure network are substances
having a crystal structure in which radicals of SiO.sub.4, e.g. polymeric
acid radicals of SiO.sub.4, and copolymeric acid radicals of SiO.sub.4 and
A1O.sub.4 are present as main components. Silicic acid radicals having
positive ions bound thereto are developed in a two-dimensional plane,
netlike manner. A more detailed explanation thereof is given in Ceramics
Handbook edited by Association of Ceramics, pp. 11-18. These substances
have crystals developed in plane layers, and a slip phenomenon occurs in
the layers because those layers are bound by a weak van der Waal's force.
The invention reduces this slip phenomenon for controlling and improving
the friction characteristics of the present friction material.
The inorganic substances having said plane, netlike crystal structure
include talc, vermiculite, aluminum hydroxide, magnesium hydroxide,
agalmatolite, kaolin, chlorite, sericite, iron hydroxide and
montmorillonite etc. in addition to mica and graphite. Particle diameters
of mica were 70 .mu.m, 100 .mu.m and 500 .mu.m and those of graphite were
60 .mu.m, 100 .mu.m and 270 .mu.m. The materials were granulated by a
granulator having a rotary pan. A two shaft extruder having an extrusion
slot with an inside diameter of 1 mm was used to form a strip which was
kneaded and compressed between two separate rollers into a sheet of 0.5 mm
thickness. In Table 2, F-3 and F-6 were granulated by the method using the
two shaft extruder and F-4 was granulated by the compression method by
using a roller, wherein F-6 was granulated after heating at 200.degree. C.
for 5 hours. The other samples were merely dried at a temperature below
the boiling point of the solvent. The resulting granulated material having
an average particle diameter of 300 .mu.m, has been obtained by
classification and grinding. Excepting F-6, the granulated materials
contained in the abraded surfaces of the disc brake pads were extended by
10% or more and those of C-1, D, E, H and I were extended by 30% or more.
FIG. 1 is a graph showing the brake noise occurrence ratios of brake pads
A-I manufactured in accordance with Table 2. The measurement of the brake
noise occurrence ratios was carried out with the A-H brake pads attached
to small-sized cars having a 2000 cc engine and running at a speed of 40
Km/h. The temperature of 40.degree. C. of the pads before braking changed
to 260.degree. C. due to deceleration by applying the brakes and from
260.degree. C. back to 60.degree. C. in one test cycle. Each test cycle
was divided into ten brake steps of 0.05 g in the range of 0.05 to 0.5 g.
In total, the measurement of the brake noise occurrence ratios was carried
out at 2200 stops in 10 test cycles.
FIG. 2 is a graph showing, in addition to the brake noise occurrence ratio
of F-1 shown in FIG. 1, the brake noise occurrence ratios measured under
the same conditions as those in FIG. 1, on the samples F-3, F-4, F-5, F-6,
and F-7. Each of these samples had the same volume percent of mica and
graphite as the sample of F-1.
FIG. 3 shows the friction coefficients .mu. of the disc pads in the test
carried out by using a dynamometer simulating a small-sized car having a
2000 cc engine in accordance with the examination standard of JASO 6914,
wherein the second resistance was 130 Km/h and the deceleration was 0.6 g.
The applied moment of inertia was 6.0 Kg.multidot.m.multidot.S.sup.2 and
brake discs having a thickness of 22 mm and an outer diameter of 250 mm
were utilized.
Referring to FIGS. 1, 2 and 3, the test results will be described. First,
it can be seen from FIGS. 1 and 3 that example B which includes a small
quantity of mica, had a high brake noise occurrence ratio. Conversely,
example I which includes a large quantity of mica had a lower brake noise
occurrence ratio as compared to example B. It can be also seen that
examples D and F each including both mica and graphite, had still lower
brake noise occurrence ratios than that of example I. The friction
coefficients .mu. of examples D and F were larger than that of example I.
It can be seen from FIG. 2 that example F-6 made to include a thermally
cured thermo-setting resin, had the highest brake noise occurrence ratio
while example F-3 which was not thermally cured had a lower ratio.
Furthermore, the brake noise occurrence ratio of example F-4 manufactured
by the granulation method and compressing by using the rollers, had a
lower brake noise occurrence ratio than that of example F-3. It can be
also seen that example F-7 which includes mica and graphite having small
particle diameters, had a brake noise occurrence ratio as low as that of
example F-3.
The above described test results will now be considered in more detail.
Mica having a smaller particle diameter would more effectively prevent
brake noise than mica having a larger particle diameter does when both
samples include the same volume of mica. The brake noise could be more
effectively prevented by blocks of mica having a smaller particle
diameter, than the mica particles uniformly dispersed in the friction
material. However, such mica blocks formed as a compound material of cured
thermosetting resin as a binder for the mica compound blocks which are
then conventionally ground, still have a relatively low brake noise
prevention effect, which means that brake noise is still substantial. This
is due to the fact that mica having a plate or scaly form is
longitudinally, laterally and diagonally arranged at random in the
friction material. Therefore, according to the invention mica needs to be
arranged approximately in parallel to the friction surface of the friction
pad in order to improve the brake noise preventing effect. The brake noise
can be more effectively prevented by mica bodies having smaller particle
diameters arranged in parallel to the friction surface. This is so because
micro separation of the mica occurs due to frictional resistance resulting
from the contact of the braking pad with the brake disc when a braking
force is applied, whereby the stick slip phenomenon is suppressed.
In addition, particle diameters of the graphite and of the mica are
preferably within the range of 150 .mu.m to 300 .mu.m or more.
At least a proportion of the flattened mica or mica and graphite in the
friction surface should have a particle diameter of not less than 500
.mu.m.
A first binder for helping the inorganic particles including mica or
graphite to agglomerate as taught by the invention, is an adhesive agent
such as molasses, sodium alginate, latex, polyvinyl alcohol cellulose,
gelatin, pitch and lignin, thermoplastic resin and thermosetting resin
which is not completely cured to form granules. Such binder may be used
singly. However, it is preferable ferable to use the first binder together
with an adhesive agent and resin in order to facilitate the granulation or
rather agglomeration of mica and graphite particles, which do not mix
together easily. Thermoplastic resin is preferred as a first binder for
the agglomeration, whereby the mixture of granular material and a second
binder forming a matrix is more fluid at the time of mixing. The first
binder is not limited to an organic binder but it may be an inorgac binder
such as sodium silicate and sodium polyphosphorate. The second binder that
forms the matrix is a phenolic resin as disclosed in present Table 3.
The volume ratio of the first binder to the non-granulated inorganic
substance is preferably 0.02:1 to 1.0:1, more preferably 0.04:1 to 0.5:1
and desirably 0.06:1 to 0.35:1 to obtain an effective agglomeration and
the formation of granules. An insufficient binder results in an
insufficient granulation or agglomeration, whereby dust is liable to be
generated. On the other hand, a too large quantity of first binder in the
friction material reduces or deteriorates the friction effect.
Granulation or agglomeration was carried out by using a Banbury mixer, a
rubber roller for roller kneading, a pressure kneader and an extruder to
obtain a block by either heat or pressure or both of them. Thereafter, the
block was dried and ground as necessary. In order to make the fluidity
larger during the formation, a grinder with a rotary pan is preferably by
which granules having a small apparent density can be obtained without
applying pressure. A spray dryer may be utilized dependent on the particle
diameter of mica and graphite. In addition, the method of compressing the
block into a thin sheet by a roll exceptionally allows mica and graphite
to be arranged in parallel directions, which effectively prevents brake
noise.
Inorganic substances having the plane netlike crystal structure as
disclosed in FIGS. 5 and 6 and suitable for forming the granules with the
help of the above mentioned first binder include, in addition to mica and
graphite, talc, vermiculite, aluminum hydroxide, magnesium hydroxide,
agalmatolite, kaolin, chlorite, sericite, iron hydroxide, montmorillonite,
etc. As mentioned, mica, when comminuted into small particles, and
graphite can produce the same effect.
The following Table 3 shows composition ratios of the materials for disc
brake pads using inorganic substances having the plane netlike crystal
structure, other than mica, according to the second embodiment of the
present invention. Table 4 shows brake noise occurrence ratios of the disc
brake pads made of materials shown in Table 3 in the brake noise test
conducted under the same conditions of measurement as that shown in FIG.
1.
TABLE 3
__________________________________________________________________________
Materials of Compositon
a-1 a-2
a-3 b-1 b-2
b-3 c-1 c-2
c-3
__________________________________________________________________________
quebracho pulp
10 10 10 10 10 10 10 10 10
copper powder
3 3 3 3 3 3 3 3 3
glass fiber 10 10 10 10 10 10 10 10 10
cashew dust 15 15 15 15 15 15 15 15 15
molybdenumdisulfide
2 2 2 2 2 2 2 2 2
phenol resin
19.25
19 17.75
19.25
19 17.75
19.25
19 17.75
calcium carbonate
33 25 10 33 25 10 33 25 10
graphite 4.5 5 7 4.5 5 7 4.5 5 7
mica
talc 2.5 10 23
aluminium hydroxide 2.5 10 23
vermiculite 2.5 10 23
magnesium hydroxide
agalmatolite
kaolin
chlorite
sericite
iron hydroxide
montmorillonite
binder for granulation
1.5 2 4.5 1.5 2 4.5 1.5 2 4.5
total 100.75
101
102.5
100.75
101
102.25
100.75
101
102.25
__________________________________________________________________________
Materials of Compositon
d-1
d-2
d-3
d-4
d-5
d-6
d-7
e-1 e-2 e-3
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quebracho pulp
10 10 10 10 10 10 10 10 10 10
copper powder
3 3 3 3 3 3 3 3 3 3
glass fiber 10 10 10 10 10 10 10 10 10 10
cashew dust 15 15 15 15 15 15 15 15 15 15
molybdenumdisulfide
2 2 2 2 2 2 2 2 2 2
phenol resin
19 19 19 19 19 19 19 18 18 18
calcium carbonate
23 25 25 25 25 25 25 12.5
2.5 7
graphite 7 5 5 5 5 5 5 4.5 4.5 5
mica 13
talc 10
aluminium hydroxide 13 13
vermiculite 10
magnesium hydroxide
10
agalmatolite 10
kaolin 10
chlorite 10 5
sericite 10
iron hydroxide 10
montmorillonite 10 10 10
binder for granulation
2 2 2 2 2 2 2 4 4 4
total 101
101
101
101
101
101
101
102 102 102
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TABLE 4
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Materials
Composition
a-1
a-2
a-3
b-1
b-2
b-3
c-1
c-2
c-3
d-1
d-2
d-3
d-4
d-5
d-6
d-7
e-1
e-2
e-3
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brake noise occurance
18
6 5 22
11
5 25
16
7 16
13
12
9 11
13
10
4 4 1
ratio %
__________________________________________________________________________
FIG. 4 is a simplified block diagram for explaining the method of
manufacturing the disc brake pads according to the invention made of
material compositions shown in Table 3. With reference to FIG. 4, the
method of manufacturing the disc brake pads shown in Table 3 will be
described in general. A more detailed description will be provided below
with reference to FIG. 13. First, as shown in step 101, granulation
materials shown in Table 3 are granulated by the granulator with a rotary
pan. Sodium alginate and polyvinyl alcohol are used as the first binder
and water is used as a dilutent to form an agglomeration of particles in
the form of granules. As shown in step 102, the conditions of forming the
disc brake pads shown in Table 3 are the same as those shown in Table 1.
The temperature for pressurization is 160.degree. C., the time for
pressurization is 10 mins. and the pressure is set such that the completed
pad may have a porosity of 10%. After the thermoformation, the pad is
heated in a furnace at 220.degree. C. for 10 hours to complete curing.
Thereafter, as shown in step 103, the pad is abraded to have a prescribed
thickness.
Referring to Tables 3 and 4, similar to mica, talc, aluminum hydroxide,
vermiculite, magnesium hydroxide, agalmatolite, kaolin, chlorite,
sericite, iron hydroxide and montmorillonite effectively lower the brake
noise occurrence ratio of a brake pad according to the invention. The
quantity of the just listed materials is preferably not larger than half
of the total quantity of the substance having the plane crystal structure
network and preferably not more than 1/5. The quantity of graphite should
not be larger than maximally 2.0 vol. with respect to the total volume of
the substance of the plane netlike crystal structure, preferably not
larger than 1.5 vol. %, preferably not larger than 1.0 vol. %. While the
increased quantity of graphite more effectively prevents brake noise, it
decreases the friction coefficient .mu..
In the present embodiment, one or more than one of mica, vermiculite,
graphite, talc, magnesium hydroxide, agalmatolite, kaolin, chlorite,
sericite, iron hydroxide and montmorillonite may be used in combination
with an organic or inorganic first binder to form granules which are used
as a part of the present friction material. The first binder for
granulation or agglomeration can be softened and fluidized by heat or both
heat and pressure in forming a friction material and the configuration of
thus formed granulated material or rather of the particle orientation in
the granules is substantially flat which is different from the original
orientation. The flat orientation of the plane netlike crystal structure
particles such as mica, makes sure that the particles in the surface of
the friction material are arranged substantially in parallel to the
friction surface, namely along the direction of the friction and
consequently, microseparation is liable to occur to effectively reduce the
brake noise of the brake. As a result of research on materials for
effectively reducing the brake noise, it was found that inorganic
particles of the plane netlike crystal including mica, vermiculite,
aluminum hydroxide and magnesium hydroxide are effective and an even
better reduction of the brake noise can be obtained by using the same
together with graphite. It is appropriate that the quantity of granulated
granules contained in the brake material is in the range of 1-35 vol. % of
the total quantity, preferably in the range of 3-30 vol. % and preferably
in the range of 5-25 vol. %.
In this case, if the quantity of granulated granules is small, the brake
noise can not be effectively prevented and conversely, if the quantity is
too large, the friction coefficient .mu. at a high speed is decreased.
Granulated mica, graphite and the like may be used together with this
granulated substance of granules. While the inorganic substances having
the plane netlike crystal structure are used in the present embodiment,
the present invention is not limited thereto and a substance having a
similar crystal structure to the plane netlike crystal structure may be
used.
FIG. 7 shows a particle 1 of an inorganic substance as disclosed above. The
particle 1 has, for example, four layers 2 interconnected along boundary
surfaces 3. Each layer of the inorganic substance has a plane network of a
crystal structure as described above with reference to FIGS. 5 and 6. When
the layers 2 are displaced relative to each other, in response to friction
forces indicated by arrows 100, the above mentioned "slip phenomenon"
occurs along the boundary surfaces 3. Each particle 1 has a somewhat
oblong, relatively flat configuration.
FIG. 8 shows one granule 4 formed by mixing the particles 1 of FIG. 7 with
a first binder 5 in which the particles 1 are enveloped or embedded. For
example, nine particles 1 may form 1 granule 4. The number of particles 1
in the granules 4 is random. The granules 4 are formed as described above.
FIG. 9 shows the result of the mixing of a second binder 6 with the
granules 4 shown in FIG. 8 and with fibrous material 7 forming a
reinforcement or filler. The deformable mixture of FIG. 9 is then molded
by, the application of pressure and/or heat to form a molded body 8 shown
in FIG. 10. The granules 4 and the fibrous material 7 are embedded in the
second binder material 6 to form the molded body 8 in such a way that all
of the granules 4 with their oblong, approximately flat configuration are
oriented in a predetermined direction which is the direction of the
friction force 100 shown in FIG. 7. The second binder is, for example,
phenolic resin as shown in Table 3. The molded body 8 has a rough surface
9 which will be the surface that is to be subjected to a grinding
operation to form the friction surface or ground surface 10 shown in FIG.
11. The friction force 100 will be applied in parallel to the friction
surface 10 so that the orientation of the oblong flat particles 1 and the
orientation of the oblong approximately flat granules 4 will extend
substantially in parallel to the friction surface 10 as shown in FIG. 11.
FIG. 12 corresponds to the illustration of FIG. 1 of U.S. Pat. No.
4,735,975 (Iwata et al.). Random shaped granules 11 are held together by a
resin binder 12 which leaves either open or closed interstices 13 between
neighboring random shaped granules 11. Such a structure 14 does not
suggest any reduction of the brake noise because neither the particles
which form the random shaped granules 11 nor the granules themselves,
suggest the orientation claimed according to the invention.
FIG. 13 summarizes the substances of the foregoing description and the
labels in FIG. 13 are self-explanatory. The fibrous material that is used
with the second binder and the granular material is listed, for example,
as copper powder, cashew dust, molybdenum disulfide, calcium carbonate,
and the like.
In the method of manufacturing the present disc brake pads the plane
netlike crystal structure of the particles in the granules formed by the
first binder, which is used without being cured, results in a
predominantly flat orientation of the mica or the like particles in the
granules, whereby a micro-separation, caused by the application of a brake
force, occurs in the friction surface of the disc brake pad. This
micro-separation is facilitated by the flat particle orientation, whereby
brake noise has been reduced. In addition, a granule of, e.g. mica formed
by granulation results in a heavy substance, so that a manufacturing
problem such as the blowing-up of mica dust has been effectively
prevented. Furthermore, since the number of particles is reduced by
granulation or agglomeration, it is possible to effectively prevent
separation, segregation and decrease of the strength of the friction
material due to insufficient mixture of a binder and mica or the like,
which is the problem in using conventional fibers as a main material for
the brake pads.
The friction material according to the present invention avoids the problem
of maintaining a hygienic environment while simultaneously effectively
preventing brake noise while still maintaining the size of the braking
force. In other words, the invention avoids a decrease of the friction
coefficient.
Although the invention has been described with reference to specific
example embodiments, it will be appreciated that it is intended to cover
all modifications and equivalents within the scope of the appended claims.
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